AB0066 ACCELERATED MONOCYTE DIFFERENTIATION AND HIGH EXPRESSION OF MACROPHAGE COLONY-STIMULATING FACTOR RECEPTOR IN THE MONOCYTES MAY BE INVOLVED IN ACCELERATED OSTEOCLASTOGENESIS IN RHEUMATOID ARTHRITIS
Authors: M. Murakami, N. Nishimoto
Journal: Annals of the Rheumatic Diseases (2023)

<h3>Background</h3> Rheumatoid arthritis (RA) is a systemic autoimmune disease characterized by chronic proliferation of synovial cells and destructive polyarthritis. Various kinds of cells are involved in the pathogenesis of RA, including myeloid cells, lymphocytes, and synovial fibroblasts. It has been reported that there are abnormal myeloid cells in bone marrow of RA patients (Ochi, <i>et al.</i>, Arthritis Res. Ther., 2007). In addition, myeloid cells differentiate into monocytes/macrophages, which can thereafter differentiate into osteoclasts that mediate bone destruction in RA. In fact, we have previously reported CD14+ monocytes differentiated from induced pluripotent stem cells (iPSCs) derived from RA patients expressed more mRNA of receptor activator of nuclear factor-kappa B (RANK) than those from a healthy donor, non-onset family member (NOF), resulting in the accelerated osteoclastogenesis (Ito, <i>et al.</i>, The 36<sup>th</sup> annual meeting of the Japanese society of inflammation and regeneration, 2015). However, the question remains if distinct monocyte differentiation besides high RANK expression may also be involved in the accelerated osteoclastogenesis in RA. <h3>Objectives</h3> To investigate whether there is distinct monocyte differentiation between a RA patient and NOF. <h3>Methods</h3> iPSCs have been established from skin fibroblasts from a RA patient. For the controls, NOF of the patient are recruited as a donor in order to adjust hereditary background as much as possible. Monocytes were induced from each iPS clone culture on feeder-free conditions using a previously reported method (Cui, <i>et al.</i>, Front. Cell Dev. Biol., 2021). Floating cells were sequentially collected on days 10, 14, 18 and 22 during induction of monocytes from iPSCs. Surface phenotypes and the expression of differentiation markers of monocytes were analyzed with flow cytometry using the corresponding antibodies. <h3>Results</h3> RA-iPSCs differentiated into CD43+ (hematopoietic marker) cells earlier than NOF-iPSCs did (the data shown in Table 1). In addition, the proportion of CD45+ in CD43+cells (myeloid progenitors) was achieved in 93.0±4.8% (RA) and 51.0±21.3% (NOF) on day 18 (<i>p=0.029</i>) (the data shown in Table 1). The proportion of CD11b+CD45+ cells (monocytes and granulocytes) derived from RA-iPSCs was not significantly different from that from NOF-iPSCs. However, the proportion of CD45<sup>high</sup> in CD11b+CD45+ cells (monocytes) derived from RA-iPSCs was significantly higher than that from NOF-iPSCs on day 18 and 22 (the data shown in Table 1). CD45<sup>high</sup> in CD11b+CD45+ cells were mostly CD14+ cells. The proportion of CD115+, macrophage colony-stimulating factor receptor (MCSF-R), in CD14+ cells induced from RA-iPSCs tended to increase compared with NOF-iPSCs as the days of differentiation progressed (the data shown in Table 1). <h3>Conclusion</h3> Hematopoietic stem cells differentiate into myeloid progenitors in monocyte differentiation in RA earlier than those in NOF. Moreover, they differentiate into more CD14+CD11b+CD45<sup>high</sup> monocytes which are likely to express more MCSF-R as compared with those in NOF. We speculate that these distinct monocyte differentiation may play in accelerated osteoclastogenesis in RA. <h3>REFERENCES:</h3> NIL. <h3>Acknowledgements:</h3> NIL. <h3>Disclosure of Interests</h3> Miho Murakami: None declared, Norihiro Nishimoto Grant/research support from: Chugai Pharmaceutical Co. and Esai Co., Ltd.,